1. Field of the Invention
The present invention generally relates to custom-fitting earplugs that are formed in situ and, more particularly, to a device and method for creating a custom-fitting earplug in the ear of the prospective user which utilizes a foaming agent that expands and fills the ear canal after its insertion in the patient's ear. These earplugs have multiple applications, including: noise suppression, ear seals for swimming and sleeping, ear canal measurement devices and casts for ear plugs and hearing aids. Furthermore, these earplugs are useful in the creation of acoustic and electronic ear devices, including: communications receiver, transmitter, and transceivers, hearing aids, hearing test transducer or probe tube, ear microphones, personal earphones (miniature loudspeaker), tuned resonating devices for sound wave modification, and other acoustic and electronic devices.
2. Description of the Prior Art
Earplugs are presently in common use in a number of activities. Airport and heavy industry personnel typically use noise-attenuating earplugs on a daily basis to prevent hearing damage. The Occupational Health and Safety Administration (OSHA) presently requires that all workers exposed to noise of 85 decibels A-weighted (dBA) time-weighted average over an eight hour day must be supplied with hearing protectors. According to recent estimates of the Environmental Protection Administration (EPA), over nine million American workers are exposed to levels above the threshold levels set by OSHA on a daily basis. In addition to industry, people often use earplugs when operating light machinery such as chain saws, when participating in sporting activities such as swimming and shooting, and when attending various spectator events such as automobile races, truck pulls, and rock concerts.
Prior art "universal fit" type earplugs typically comprise a foam, mineral fiber, wax, or putty-like (e.g., Swedish Wool) material which is either unencapsulated or sheathed in a thin, smooth outer skin. Outside the wearer's ear the plugs may have a cylindrical or other pre-formed shape. These plugs are often termed "universal fit" because they are intended to adapt to the contours of any person's ear canal to provide hearing protection. To install the "universal fit" earplug, the wearer must first compress and/or form the plug by kneading, wadding or rolling it up and then position the plug in his or her ear canal. In the case of the foam earplug, the plug must be inserted before it expands. After insertion, the "universal fit" plug is supposed to assume the natural contours of the ear canal by expansion therein. Typical examples of "universal fit" foam earplugs are shown and discussed in U.S. Pat. No. 4,160,449 to Wade, U.S. Pat. No. 4,459,247 to Rothemund, and U.S. Pat. No. 4,434,794 to Leight.
Universal fit earplugs suffer from a variety of problems. First, the plugs are difficult for many individuals to insert properly. If the plug is incorrectly formed by the user as it is inserted in the ear canal, wrinkles and voids may develop that allow sound leakage to the user's eardrum, thereby reducing the protective effectiveness of the plugs to the wearer. Second, some of the plugs typically are larger than people may need because the commercial vendor has designed the plugs to fit ear canals that are larger than average in hopes of accommodating a wide range of users. Third, some users find universal fit earplugs to be uncomfortable.
Custom-molded earplugs can be an attractive alternative to universal fit earplugs and have advantages in their comfort, more reliable fit, and lower long-term costs due to longer usable life. Also, custom-molded earplugs may offer certain hygiene advantages in dirty environments since the user does not have to compress or form them with their fingers prior to insertion. Custom-molded earplugs are essentially a mold of the wearer's ear canal and concha of the outer ear. Hence, the earplugs can be precisely positioned in the ear by the wearer so that his or her ear canal is not subjected to undue pressure when the plugs are installed and because of the personalized fit, sound is effectively blocked by the plugs. Some custom-molded earplugs are made by making a positive casting of the ear canal first, then making a negative mold, and finally making the earplug from the negative mold.
U.S. Pat. No. 3,097,059 to Hoffman discloses a method of making earplugs in situ which eliminates the need for making negative and positive casts. The earplug is fabricated by depositing a mass of acrylic resin in the wearer's ear and allowing the acrylic to cure therein. U.S. Pat. Nos. 3,696,090, 3,782,379, 3,897,376, and 3,925,277 to Lampe disclose two part room temperature vulcanizable rubber compositions which are used to form earplugs in situ in a manner similar to that described in Hoffman.
Casting an earplug in situ using a self-curing resin is not an ideal method for creating a custom-molded earplug. A doctor or a trained technician will be required to make the mold since the mold's manufacture requires a highly viscous resin or putty to be deposited deep in the patient's ear. The objective when taking the earmold is to obtain an impression which follows all inner contours of the ear canal and which has no voids or creases due to the trapped air pockets. Packing the resin in the ear canal to meet this objective can be very painful to the patient. During packing, air is trapped between the tympanic membrane (eardrum) and the viscous resin. Because of the viscosity of the resin, air cannot easily escape the ear canal through or around the resin; therefore, external pressures exerted to pack the resin in the ear will be transferred to the tympanic membrane and to middle ear structures. The viscous resin can be forced into the ear canal using a large syringe. Alternatively, a paste-like resin material can be inserted into the ear canal using a putty knife or the doctor's thumb to force the resin down into the ear canal. After the resin is added to the ear, it may be necessary to manually apply some pressure from outside the ear to assure that the resin hardens within the canal. The patient must sit motionless, without jaw movement, for several minutes until the mold solidifies.
Besides severe pain being caused to many patients, casting an earplug in situ also suffers from the common problem of voids being formed therein which reduce the effectiveness of the final earplug produced. This results in the need for taking multiple impressions. For example, if the resin is not packed into the user's ear tightly enough, air pockets will be created in spaces where the resin does not contact the walls of the ear canal or invisible voids may occur within the resin structure itself. British Patent 2,084,072 to Carr addresses this problem by providing additional coatings on the outside surface of the plug until a perfect impression is made. Such a tedious process for forming an earplug is not acceptable.
British Patent 2,090,535 to Fekry discloses an improved method for creating an earplug in situ. A water swellable insert is first installed in the ear, then water drops are added to the insert causing it to expand inside the ear to a preset shape. While the insert described in the patent may avoid the disadvantage of pain to the wearer of custom-molding earplugs (assuming the preset size does not exert pressure on the ear canal walls), it does not create a custom-fitting earplug in its expanded state. Rather, the insert expands to one preset shape and would suffer from the same disadvantages discussed above in conjunction with universal fit type earplugs.
French patent 1,559,694 to Avot discloses an earplug which comprises a deformable capsular enclosure containing liquid precursor components separated by a partitioning element. Finger pressure brings the two liquids separated by the partition together to create a foam which expands within the ear. The Avot earplug suffers from the problem that it has no structural rigidity and will tend to wad up on initial insertion if it is extracted and re-installed in the ear. Furthermore, being a liquid state prior to initial insertion which will determine its initial formation, and having no structural rigidity, the earplug capsule will not be insertable deep enough into the ear canal to obtain an accurate impression.